The quality of how colors are reproduced is called color rendering. Line spectra have very good color rendering. Line spectra allow only a single color to be perceived well. Multi-line spectra render several colors of the respective spectrum well, but color rendering is weaker in the intermediate ranges. Blue and green colors appear comparatively gray and dull in warm white incandescent light despite excellent color rendering. However, these color tones appear clear and luminous in the light of daylight white fluorescent lamps – despite poorer color rendering. With the rendering of yellow and red color tones, this phenomenon of weakening or intensifying of the color effect is reversed.
Because the eye is able to adapt to light of the most different color temperatures, the color rendition must be determined dependent on the color temperature. Tungsten halogen lamps feature very good color rendition. The rendition quality of fluorescent lamps and metal halide lamps ranges from good to average. The degree of color distortion against a reference light source is indicated using the color rendition index Ra or the color rendition grading system. The color rendition index is only used for white colors of light.